WITH regard to colour, the disquisition is almost infinite: but I conceive the principles laid down in the beginning of this part are sufficient to account for the effects of them all, as well as for the agreeable effects of transparent bodies, whether fluid or solid. Suppose I look at a bottle of muddy liquor, of a blue or red colour; the blue or red rays cannot pass clearly to the eye, but are suddenly and unequally stopped by the intervention of little opaque bodies, which without preparation change the idea, and change it too into one disgreeable in its own nature, conformably to the principles laid down in sect. 24. But when the ray passes without such opposition through the glass or liquor, when the glass or liquor is quite transparent, the light is sometimes softened in the passage, which makes it more agreeable even as light; and the liquor reflecting all the rays of its proper colour evenly, it has such an effect on the eye, as smooth opaque bodies have on the eye and touch. So that the pleasure here is compounded of the softness of the transmitted, and the evenness of the reflected light. This pleasure may be heightened by the common principles in other things, if the shape of the glass which holds the transparent liquor be so judiciously varied, as to present the colour gradually and interchangeably, weakened and strengthened with all the variety which judgment in affairs of this nature shall sug gest. On a review of all that has been said of the effects as well as the causes of both, it will appear, that the sublime and beautiful are built on principles very different, and that their affections are as different: the great has terror for its basis; which, when it is modified, causes that emotion in the mind which I have called astonishment; the beautiful is founded on mere positive pleasure, and excites in the soul that feeling which is called love. Their causes have made the subject of this fourth part.